The goal of this proposal is, based largely on our previous studies, to develop techniques to degrade sediment PCBs by enhancing anaerobic dechlorination and combining it with aerobic biodegradation using indigenous microbial populations, and to determine the fate and ecological impact of sediment PCBs in the St. Lawrence River near the Massena Superfund site. Specifically, we will determine: (1) factors enhancing in situ dechlorination in highly contaminated sediments; through a comparative study of the General motors (GM) and Reynolds sites, we will determine (a) whether these differences are due to differences in microbial competence or sediment composition, (b) what determines the end point of in situ dechlorination at each site, (c) how to accelerate in situ biotransformation, and (d) the extent of detoxification by dechlorination with the assays of MCF-7 human breast cancer cell growth and catecholamines in rat brain slices. Experiments will be carried out in laboratory incubation studies with native sediments. (2) The threshold concentration in areas below the point source of contamination which may set the residual PCB level after dechlorination. We will also determine the dechlorination potential using single congener assays, microbial biomass and community characteristics with the phospholipid fatty acid and 16S rRNA hybridization techniques. (3) How to maintain and enhance dechlorinating activities in dredged sediments. Dredging and encapsulation are commonly used to remediate contaminated sites and the most heavily contaminated sediments at the GM site will also be dredged soon. Our studies of dredged Hudson River sediments showed that dechlorination ceased at an early stage after encapsulation and the sediments no longer harbored dechlorinating organisms. Using a simulated disposal facility in the laboratory, we will determine the time course of change in dechlorination activity and microbial biomass and also how dechlorination activity is affected by various conditions including the moisture content and organic matter. (4) how to degrade dechlorination products with indigenous aerobic microorganisms. Aerobic PCB-degrading bacteria will be isolation from the surface layers of the same sediments used in the dechlorination studies using the biphenyl-enrichment technique. The isolates will then be determined for their effectiveness to degrade the dechlorination products accumulated in sediments from experiments in Specific Aims 1 and 3. The degradation characteristics and optimum conditions for degradation will also be determined. We will also determine whether aerobic degradation can be induced in these sediments without inoculating isolates.